This invention relates to a valving system for a spring brake actuator which incorporates an anti-compounding valve, and pressure test points into a valve assembly for communicating and exhausting pressurized air to the spring brake chambers.
Spring brake actuators are utilized by heavy vehicles to control the application of the brake. Generally, two brake chambers are housed together and connected to a vehicle brake. One brake chamber is supplied with air to actuate the brake when the truck operator steps on the brake pedal. This side, known as the "service brake" is supplied with air to force a push rod outwardly of a brake chamber and set the vehicle brake.
A second brake chamber is positioned atop the service brake chamber and supplied with its own push rods and a large power spring. This brake chamber, known as the parking or emergency brake chamber, selectively forces its push rod against the service push rod to set the brake whenever the supply of pressurized air to the parking brake chamber is exhausted. Thus, should the air brake system air supply fail, the power spring will move the spring brake push rod outwardly to set the brake. Also, when the vehicle is parked, a parking brake valve is actuated to exhaust air from the parking brake chamber allowing the power spring to move its push rod outwardly and set the brake.
In some instances, when the parking brake is set, the driver may step on the brake pedal. This would cause both chambers of the brake to be actuated. The force on the brake would be undesirably high. This is known as "compounding," and is undesirable. To address the problem of compounding brake force, many air brake systems are provided with valves in the air supply lines which prevent the dual application of both the service and emergency brakes.
Another feature of spring brakes is the provision of "test points." These are connections on the supply lines for the pressurized air at which the pressure of the air supply can be tested.
Prior to this invention, both the anti-compounding valves and the test points have been supplied as separate parts which are not incorporated into the body of the spring brake actuator.